^Paul R. Laird Towards a history of the Spanish villancico 1997 "There is some confusion as to the identity of Matias Ruiz. A textual concordance between a pliego suelto from Encarnación in 1677 and the music manuscript of "En la carcel de Belen" at the Escorial make it likely that this is the Matias Ruiz who was chapelmaster at Encarnación between 1676 and 1678"
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